PSI - Issue 42

Mushfiq Hasan et al. / Procedia Structural Integrity 42 (2022) 1169–1176 Mushfiq Hasan et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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damage. A secondary electron beam of 15 to 20 kV was employed for surface inspection with a probe current of 30 Ampere. Moreover, backscatter electron mode was used for some EDS analysis.

Fig. 1: Twin disk micropitting rig

2.3. Test matrix The test cases map which was followed in three phases is given below. Hamrock and Dowson’s empirical equation (11) was used to predict minimum film thickness throughout the experiments.

Table 1: Experimental Test Cases

Test no.

SRR

Pinion (Crown)

Wheel (Flat)

Film Thickness (µm)

Remarks

Parameters

Slide to Roll Ratios SRR1/SRR2/SRR3= -0.25/-0.35/-0.45

1 2 3 4 5 6 7 8 9

SRR 1 SRR 1 SRR 2 SRR 3 SRR 1 SRR 1 SRR 1 SRR 1 SRR 1 SRR 1 SRR 1 SRR 1

Ra1 Ra1 Ra1 Ra1 Ra1 Ra1 Ra1 Ra3 Ra3 ST1 ST1 ST2

Ra1 Ra1 Ra1 Ra1 Ra1 Ra4 Ra3 Ra3 Ra3 ST 1 ST 1

0.19 0.19 0.19 0.19 0.19 0.23 0.16 0.14 0.14

Repetition

Repetition

Roughness Ra1/Ra2/Ra3/Ra4 = 0.3/0.4/0.5/0.2 µm

Repetition test with intervals

Surface Treatments NB: treated on 0.5 µm surface

10 11 12

- - -

Repetition

ST 2

2.4. Test sample and lubricants One pair of cylindrical-shaped disks with transverse surface lay was used in each test. The disks were made of through hardened bearing steel material 100Cr6) which is widely used for high fatigue applications. To achieve elliptical point contact of high pressure under reasonable load, one of the disks was crowned (Rx = 45mm) and another one has a flat surface (Rx= infinite). So, the disks are referred to as crowned and flat disks in this article. As a test lubricant, a fully formulated PAO based oil was used in all of the experiments. The kinematic viscosity of the lubricant was 6.3mm 2 /s and 27.6 mm 2 /s at 100⁰C and 40⁰C respectively. Tests were performed at 80⁰C bulk temperature across this study. 2.5. Post-processing Samples were cleaned in an ultrasonic bath with a solvent at the end of each test to remove debris and oil residue. Thus, ensuring better imaging during optical interferometer measurements. A 2.75x lens with a 1x field of view was